An engine of a vehicle may be started while a transmission coupled to the engine is in gear. By starting the engine while the transmission is in gear, it may be possible to respond in a timely manner to a request to launch a vehicle from rest. However, starting an engine while a transmission coupled to the engine is in gear also presents vehicle drivability issues. For example, if the engine is started and it produces more than a desired amount of torque at vehicle wheels, vehicle drivability may degrade. One way to control engine torque through a vehicle driveline is to control torque converter impeller speed. By limiting torque converter impeller speed, it may be possible to control driveline torque and improve vehicle drivability. However, it may be challenging to provide consistent engine speed run-up from cranking speed to idle speed during engine starting since cylinder air charge may be large during engine starting while engine intake manifold pressure is high.
The inventors herein have recognized the above-mentioned issues and have developed an engine starting method, comprising: rotating an engine to a cranking speed; adjusting engine speed to a sole desired run-up speed greater than the cranking speed and less than an idle speed; and after the engine speed is held at the desired run-up speed for a desired period, adjusting engine speed to the idle speed.
By adjusting an engine speed to a sole engine run-up speed during engine starting, it may be possible to reduce the possibility of overshooting a desired engine speed during engine run-up to idle speed. In particular, an engine actuator may be operated to adjust engine speed to a sole run-up speed. And after the engine speed is held at the desired run-up speed for a desired period, the actuator may be adjusted such that engine speed is adjusted to an idle speed, where the idle speed is greater than the engine run-up speed and where the engine run-up speed is greater than engine cranking speed. Controlling engine speed to a sole engine run-up speed, holding engine speed at the desired run-up speed for a desired period, and ramping engine speed to a desired engine idle speed may improve vehicle launch smoothness and consistency as compared to attempting to lower an engine speed gradient during engine starting.
The present description may provide several advantages. In particular, the approach may improve engine starting by improving engine speed control during engine starting. Further, the approach may reduce engine emissions by providing consistent engine starts. Further still, the approach may improve vehicle drivability.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.